A common method of recovering valuable metals from ores and concentrates is by leaching with a mineral acid. By way of example, rare earth metals are generally recovered from bastnaesite by leaching the host rock with hydrochloric acid. Uranium can be recovered from uranium-containing host rock by leaching with phosphoric acid. Copper, beryllium, nickel, iron, lead, molybdenum, aluminum, and manganese can be recovered from host rock by leaching with nitric acid. Copper, beryllium, nickel, iron, lead, molybdenum, aluminum, germanium, uranium, gold, silver, cobalt, and manganese can be recovered from host rock by leaching with sulfuric acid or hydrochloric acid.
While leaching is effective in dissolving valuable metals, a number of obstacles are encountered. Hydrometallurgical processes require water. Water may be available only in limited quantities. The available water is often saline. Furthermore, any process water generated must be suitable for disposal. Typically, the process water is disposed of using evaporation ponds, which can be expensive to construct and deleterious to the environment. Evaporation ponds have particularly long term environmental footprints. Furthermore, the leaching process requires electrical energy. Electrical energy can be difficult or expensive to obtain, particularly when the deposit is in a remote location. This generally requires the mine operator to construct, at high capital and operating costs, adequate power generation facilities.